Ecosystem Geography

Aim To evaluate the influence of environment and biogeographical region, as a proxy for historical influence, on the ecological structure of Holarctic communities from similar environments. It is assumed that similarities among communities from similar environments in different realms are the result of convergence, whereas their differences are interpreted as being due to different historical processes.Location Holarctic realm, North America and Eurasia above 25°N.Methods Checklists of mammalian species occurring in 96 Holarctic localities were collected from published sources. Species were assigned to one of 20 functional groups defined by diet, body size and three-dimensional use of space. The matrix composed of the frequencies of functional groups in the 96 localities is used as input data in a correspondence analysis (CA). The localities are classified into nine groups according to Bailey's ecoregions (used as a surrogate of regional climate), and the positions of the communities in the dimensions of the CA are compared in relation to ecoregion and realm. Partial regression was used to test for the relative influence of ecoregion and realm over each dimension and to evaluate the effect of biogeographical realm on the variation in the factor scores of the communities of the same ecoregion. ResultsIn some cases, mammalian communities from areas with similar regional climates exhibit convergence in community structure, irrespective of the biogeographical realm where they are located. However, all of them are clearly subdivided into Nearctic and Palearctic subsets. Differences in the composition of the regional pools only partially explain differences in local communities between realms.Main conclusions Holarctic mammalian communities from regions with widely different climates differ in ecological structure irrespective of their biogeographical location. On the other hand, the structures of Nearctic and Palearctic communities from regions of similar climate radically differ in some features. Thus, although present climatic conditions influence community structure, contingent historic processes associated with each region also play a major role in determining community structure.

Section: Discussionmentioning

confidence: 99%

“…Bailey's ecoregions (see description in Bailey, 1996) have been used as a proxy for environmental factors. This worldwide hierarchical classification system regionalizes the continents in areas of similar climate, vegetation structure and soil, regardless of biogeographical differences in species composition.…”

Section: The Data Basementioning

confidence: 99%

An evaluation of the influence of environment and biogeography on community structure: the case of Holarctic mammals

Rodrı́guez

Hortal

Nieto

2006

“…Three hundred and five BBS routes were identified within the ‘Great Plains’, defined as the 17 ecoregional sections in the Great Plains–Palouse Dry Steppe Province, Great Plains Steppe Province, Pecos Valley, Texas High Plains, and Rolling Plains of the Southwest Plateau and Plains Dry Steppe and Shrub Province of the Bailey ecoregional classification system (Bailey, 1995, 1996) (Fig. 1).…”

Section: Methodsmentioning

confidence: 99%

A probability‐based analysis of temporal and spatial co‐occurrence in grassland birds

Veech¹

2006

To date, most studies of species co-occurrence have involved the analysis of static species presence-absence matrices. These analyses are often contentious: researchers sometimes disagree about how to construct the randomized matrices that are required for testing the statistical significance of observed co-occurrence patterns (Gotelli, 2000). There are also a variety ABSTRACT Aim To test for non-random co-occurrence in 36 species of grassland birds using a new metric and the C-score. The analysis used presence-absence data of birds distributed among 305 sites (or landscapes) over a period of 35 years. This analysis departs from traditional analyses of species co-occurrence in its use of temporal data and of individual species' probabilities of occurrence to derive analytically the expected co-occurrence between paired species.Location Great Plains region, USA.Methods Presence-absence data for the bird species were obtained from the North American Breeding Bird Survey. The analysis was restricted to species pairs whose geographic ranges overlapped. Each of 541 species pairs was classified as a positive, negative, or non-significant association depending on the mean difference between the observed and expected frequencies of co-occurrence over the 35-year time-span. ResultsOf the 541 species pairs that were examined, 202 to 293 (37-54%) were positively associated, depending on which of two null models was used. However, only a few species pairs (<5%) were negatively associated. An additional 89 species pairs did not have overlapping ranges and hence represented de facto negative associations. The results from analyses based on C-scores generally agreed with the analyses based on the difference between observed and expected co-occurrence, although the latter analyses were slightly more powerful.Main conclusions Grassland birds within the Great Plains region are primarily distributed among landscapes either independently or in conjunction with one another. Only a few species pairs exhibited repulsed or segregated distributions. This indicates that the shared preference for grassland habitat may be more important in producing coexistence than are negative species interactions in preventing it. The large number of non-significant associations may represent random associations and thereby indicate that the presence/absence of other grassland bird species may have little effect on whether a given focal species is also found within the landscape. In a broader context, the probability-based approach used in this study may be useful in future studies of species co-occurrence.

“…The distinctiveness of the vegetation in the New England forest likewise depends on the scale of resolution. At a continental scale, plant geographers have traditionally viewed the region as reflecting a gradual transition between climatic ‘biomes’ or floristic ‘provinces’, blending the northern coniferous forest with the southern deciduous forest (Merriam, 1898; Gleason & Cronquist, 1964; Bailey, 1996). At an increased resolution, the vegetation of the north‐eastern United States has been viewed either as a distinct transitional ‘formation’ supporting a suite of endemic species (e.g.…”

Section: Vegetation Structurementioning

confidence: 99%

The forests of presettlement New England, USA: spatial and compositional patterns based on town proprietor surveys

Cogbill

Burk

Motzkin

2002

188

196

Aim This study uses the combination of presettlement tree surveys and spatial analysis to produce an empirical reconstruction of tree species abundance and vegetation units at different scales in the original landscape.Location The New England study area extends across eight physiographic sections, from the Appalachian Mountains to the Atlantic Coastal Plain. The data are drawn from 389 original towns in what are now seven states in the north-eastern United States. These towns have early land division records which document the witness trees growing in the town before European settlement (c. seventeenth to eighteenth century AD).Methods Records of witness trees from presettlement surveys were collated from towns throughout the study area (1.3 · 10 5 km 2 ). Tree abundance was averaged over townwide samples of multiple forest types, integrating proportions of taxa at a local scale (10 2 km 2 ). These data were summarized into genus groups over the sample towns, which were then mapped [geographical information system (GIS)], classified (Cluster Analysis) and ordinated [detrended correspondence analysis (DCA)]. Modern climatic and topographic variables were also derived from GIS analyses for each town and all town attributes were quantitatively compared. Distributions of both individual species and vegetation units were analysed and displayed for spatial analysis of vegetation structure. ResultsThe tally of 153,932 individual tree citations show a dominant latitudinal trend in the vegetation. Spatial patterns are concisely displayed as pie charts of genus composition arrayed on sampled towns. Detailed interpolated frequency surfaces show spatial patterns of range and abundance of the dominant taxa. Oak, spruce, hickory and chestnut reach distinctive range limits within the study area. Eight vegetation clusters are distinguished. The northern vegetation is a continuous geographical sequence typified by beech while the southern vegetation is an amorphous group typified by oak.Main conclusions The wealth of information recorded in the New England town presettlement surveys is an ideal data base to elucidate the natural patterns of vegetation over an extensive spatial area. The timing, town-wide scale, expansive coverage, quantitative enumeration and unbiased estimates are critical advantages of proprietor lotting surveys in determining original tree distributions. This historical-geographical approach produces a vivid reconstruction of the natural vegetation and species distributions as portrayed on maps. The spatial, vegetational and environmental patterns all demonstrate a distinct Ôtension zoneÕ separating Ônorthern hardwoodÕ and Ôcentral hardwoodÕ towns. The presettlement northern hardwood forests, absolutely dominated by beech, forms a continuum responding to a complex climatic gradient of altitude and latitude. The oak forests to the south are distinguished by non-zonal units, probably affected by fire. Although at the continental scale, the forests seem to be a broad transition, at a finer scale they respond to ...